1. Field of the Invention
The present invention relates to a toner and a developer for use in an electrophotographic copying machine, facsimile machine, and printer.
2. Discussion of Background
Conventionally, fixing of a toner image is usually achieved by the application of heat.
According to the principle of toner image fixing by means of heat application, a toner is softened or melted when heat is applied to the toner in an image fixing unit. The toner can be fixed to paper in such a way that the softened or melted toner is embedded in fibers of paper because pressure is also applied to the toner in the image fixing unit. Or, the surface of the softened or melted toner tends to become sticky by the application of heat, so that the toner can be fixed to the paper.
In light of the toner fixing mechanism mentioned above, the melting point or softening point of a resin for use in a toner composition is required to be equal to or lower than the image fixing temperature.
In recent years, there is an increasing demand for energy saving from the viewpoint of environmental protection. The energy which may be used in the image fixing unit is now being restricted. In order to decrease the energy for image fixing, there is no choice in fact but to lower the image fixing temperature that is set in the image fixing unit. Consequently, a resin with a low melting point is necessarily employed for the toner composition to cope with the image fixing unit of which the image fixing temperature is lowered. However, the resin with a low melting point tends to readily soften, so that toner particles containing the above-mentioned resin often causes caking during storage. Further, because toner particles containing such a low-melting point resin are provided with adhesive properties, interaction between the toner composition and an external additive deposited on the toner particles tends to change with time. As a result, the physical properties of the obtained toner are changed and the preservation stability of the toner is impaired.
In a developer unit, there occurs a so-called spent toner phenomenon, namely, a softened or melted toner is deposited on the surface of a carrier. Further, the toner tends to adhere to the surface of a development roller to produce a toner filming phenomenon, and the toner is easily deposited on a doctor blade in the developer unit.
Furthermore, after completion of image fixing, image-bearing sheets unfavorably stick to each other, which is referred to as a blocking phenomenon, depending on the environmental conditions.
In addition to the above, there also occurs a problem in the course of preparation of toner particles. When the conventional low-melting point resin is contained in a toner composition, it is difficult to satisfactorily pulverize the toner composition and the toner composition is apt to stick to the inner wall of a pulverizer in the pulverizing step because of excessively soft resin contained in the toner composition.
Accordingly, it is therefore a first object of the present invention to provide a toner capable of coping with a lower image fixing temperature than the conventional image fixing temperature to achieve energy-saving, exhibiting excellent preservation stability, producing no change with time in the interaction between the toner and an external additive, and causing no problems of the spent toner phenomenon and toner filming phenomenon. Further, the first object is to provide toner particles which can be obtained by efficiently pulverizing a toner composition and a toner capable of producing toner images with preservation stability after the toner is fixed to an image receiving member.
The first object of the present invention can be achieved by a toner for electrophotography comprising a coloring agent and a binder which comprises a wax and an ethyl polysaccharide.
It is preferable that ethyl polysaccharide comprise D-glucose units linked together by a linkage of 1,2-, 1,3-, 1,4-, or 1,6-glycosidic bond with an xcex1 configuration, or by a linkage of 1,2-, 1,3-, 1,4- or 1,6-glycosidic bond with a xcex2 configuration, with at least one alcohol hydroxyl group in each of the D-glucose units being ethyl-etherified.
The above-mentioned toner may be fixable at a temperature lower than a melting point of the ethyl polysaccharide and higher than or equal to a melting point of the wax.
A second object of the present invention is to provide a developer for electrophotography.
The second object of the present invention can be achieved by a one-component developer for electrophotography comprising a toner which comprises a coloring agent and a binder comprising a wax and an ethyl polysaccharide. Alternatively, the second object of the present invention can be achieved by a two-component developer comprising a carrier and the above-mentioned toner.
A third object of the present invention is to provide a developer container for storing a developer therein.
The third object of the present invention can be achieved by a developer container containing the above-mentioned one- or two-component developer for electrophotography.
A fourth object of the present invention is to provide an image forming apparatus.
The fourth object can be achieved by an image forming apparatus comprising a developer unit which comprises developer storage means for storing a developer therein and developer supply means for supplying the developer to a latent-image bearing surface, wherein the developer may be a one-component developer comprising a toner comprising a coloring agent and a binder which comprises a wax and an ethyl polysaccharide, or a two-component developer comprising the above-mentioned toner and a carrier.
A fifth object of the present invention is to provide a process unit with a developer unit.
The fifth object can be achieved by a process unit comprising a developer unit which comprises developer storage means for storing a developer therein and developer supply means for supplying the developer to a latent-image bearing surface, wherein the developer may be the above-mentioned one-component developer or two-component developer.